The present invention relates to a method of manufacturing a semiconductor device, and more specifically relates to a method for forming an electrode and its protection film on the semiconductor device.
In semiconductor devices, a poly-crystalline silicon film is widely used as an electrode material, gate electrode material and wiring material (hereinafter collectively referred to as "electrode material"). Recently, an electrode material with lower resistivity has been required due to needs for semiconductor devices with higher speed and lower power consumption. To meet the requirement, a film lamination (hereinafter referred to as "polycide film") comprised of a poly-crystalline silicon film and a metal silicide film with high melting point has been used very often. FIGS. 3(a)-3(f) shows a manufacturing method for a semiconductor device according to the prior art by way of sectional views. In FIGS. 3(a)-3(f), each sectional view corresponds to a manufacturing step of a MOSFET, especially around its gate electrode.
Now, the conventional manufacturing steps will be explained with reference to FIGS. 3(a)-3(f). At first, a gate insulation film 2 is formed on a silicon substrate 1. A poly-crystalline silicon film 3 is laminated on the gate insulation film 2 by, for example, a CVD method under reduced pressure at 650.degree. C. Then, a heat treatment is conducted, e.g. at 900.degree. C., for facilitating crystallization of the poly-crystalline film 3. Then, a wolfram silicide film (hereinafter referred to as "WSi film") 4 as a metal silicide film with high melting point is laminated on the poly-crystalline film 3, e.g. by a sputtering method (FIG. 3(a)). Then, the polycide film is patterned with a shape of a gate electrode and etched by a photo-etching technique (FIG. 3(b)). Then, a surface of the laminated film is oxidized at 800.degree. to 1000.degree. C., and the WSi film 4 is crystallized simultaneously to consume excessive silicon atoms in the WSi film 4 by oxidation. Up to this point, sheet resistance of the WSi film 4 has been lowered to 5 to 6 .OMEGA./.quadrature. from sheet resistance of 40 to 50 .OMEGA./.quadrature..
Then, an inter-layer insulation film 5 is formed on the entire surface (FIG. 3(c)). Then, side walls 6 are formed on the side faces of the polycide film (gate electrode) by etching back (FIG. 3(d)). Since an oxidizing film on a source region, a drain region and the gate electrode has been completely removed, an oxidizing film 7 is formed on the entire surface as the protection against ion implantation prosecuted later (FIG. 3(e)). The oxidizing film 7 is formed, for example, by oxidation at 800.degree. to 1000.degree. C. Then, a fundamental MOS structure is obtained by implanting impurity ions in the source region 8 and the drain region 9 (FIG. 3(f)). Then, the MOSFET is completed by disposing an electrode on each region.
According to the manufacturing method described above, the crystallized WSi film 4 exists on the top of the etched back gate electrode. When this construction is exposed to a high temperature oxidizing environment, the surface of the WSi film 4 is anomalously oxidized, which often causes strain accumulation in the WSi film 4 and its pealing off from the poly-crystalline silicon film 3. To avoid this, the anomalous oxidation is prevented by forming an amorphous structure on the surface of the WSi film 4 by ion implantation or injection prior to the oxidation, or by capping the gate electrode surface with an oxidizing film formed by a low temperature CVD method (under atmospheric pressure, under reduced pressure, or with plasma) at around 400.degree. C. prior to the oxidation.
However, the former method tends to damage the exposed source and drain regions by the ion implantation and to cause leakage of the transistor. In the latter method, the cap oxidizing film once formed by the low temperature CVD method is heat treated at high temperature. This heat treatment causes shrinkage of the cap oxidizing film, which exerts stress to the WSi film 4. Though the stress may not cause pealing off of the WSi film 4, the stress may cause lowering of adhesive force of the WSi film 4 with the poly-crystalline silicon film 3. This weak adhesion of the WSi film 4 with the poly-crystalline silicon film 3 causes serious problems on the reliability of the semiconductor devices.
In view of the foregoing, an object of the present invention is to provide a method of manufacturing a highly reliable semiconductor device which is provided with a polycide electrode having a metal silicide film with high melting point which shows excellent adhesion with and does never peals off from the poly-crystalline silicon film 3.